The present invention relates to the testing of large scale integrated circuits. Specifically, a programmable timing generator is described, capable of generating a plurality of pulse signals having selectable pulse positions.
Automatic high-speed testing devices have been developed to test large-scale integrated circuits on an automatic basis. Typically, a large scale integrated circuit made from the MECL bipolar technology would include 10,000 bipolar gates which are to be tested in order to verify the circuit's operation. These testing devices generally include pin electronic circuitry which provides driving pulses for each pin of the circuit under test, as well as detects responses from other pins under test. Under control of a master program, the automatic tester will exercise the pins by supplying a different sequence of pulses to a plurality of pins, each sequence timed with respect to each other. The response of the electronic circuit to these sequences of pulses is measured by the pin electronics.
These automatic testing devices are organized on the basis of test cycles for a group of pins of the circuit under test. Typically, one test cycle for a given pin of an electronic circuit under test is exercised, followed by subsequent test cycles. These test cycles include applying a plurality of sequential test pulses to a set of pins timed with respect to each other and to a system clock. Once a test cycle, typically in the 40 nanosecond range, is completed, a subsequent test cycle must be effected.
In the prior art, a typical technique for generating the required pulses for the pin electronics is accomplished by decoding a clock driven counter with a register and exclusive OR circuitry. These dedicated counter circuits and decoding circuitry do not lend themselves to providing the multiplicity of pulse combinations necessary to completely test an integrated circuit having state of the art device density. Also, some of the architecture involved in generating the required timing signals limits the accuracy of pulse generation, thus limiting the capabilities of effective testing of the large-scale integrated circuit.